The people of Hador were of what we should describe as a Scandinavian type; they were nearly all tall, blue-eyed and fair haired...
The people of Bëor ... bear a decided resemblance to the Brythonic Celts, and the woodland people of Haleth to the Finns.
"The Abyss and the Critics" p.137
As a bit of a reminder: the Dunedain are descended chiefly from the line of Bëor, with Sindarin admixture. The Rohirrim from Hador of course.
I still need to do a bit of re-reading to remember the rest, but it's an interesting guide to imagining our heroes nonetheless.
I fear I don't know where the author found that reference, but it's a chapter on the Children of Hurin, so I would imagine in Christopher Tolkien's explanatory notes on that work.